The application of advanced illumination models is known to support depth perception. However, in the context of volume rendering gradient-based shading models are still the standard. This is due to the fact that the computation of more advanced lighting effects is expensive, and therefore has a strong impact on rendering performance. Nevertheless, interactive frame rates are important for both, the interactive design of visual representations as well as the exploration process. We present an interactive volumetric lighting model, which simulates scattering and shadowing to generate high quality images. Besides the superior image quality as compared to gradient-based shading, in many cases we also achieve higher frame rates. To evaluate our model we have conducted a user study in which the participants had to perform depth perception tasks. The results of this study indicate that depth perception is significantly improved, when comparing our illumination model to conventional gradient-based volume shading. Additionally, since our volumetric illumination model is not based on a gradient computation, it is also less sensitive to noise and therefore also applicable to imaging modalities suffering from a low signal-to-noise ratio, such as magnetic resonance imaging or 3D ultrasound.